Reunion registries are an excellent tool that can be used to reunite adoptees with birth family. An adoptee or a birth parent can register what information they have, whether it's a little or a lot, and that data is saved while it waits for a match. You should include info such as date of birth, name of the hospital the birth took place at, the delivering doctor and/or the attorney used, as well as any other info you might have. The more information the better.
Some adoption registries are done entirely online. You enter your info and someone else can come along and search for it. Other registries are active, meaning you register with them by mail or online and if the other party registers as well, then the employees make contact to reveal the match. Private, non-profit organizations run some of the registries, while others are government run.
I always recommend that people starting an adoption search start with the registries. The oldest one is the International Soundex Reunion Registry. The others ones I suggest are registry.adoption.com and reunionregistry.org. Most states also have an adoption registry of their own. You should definitely search for the registry in the state your adoption took place in. A reunion registry can be much faster than a DNA test if the person you are looking for has already been there.
Many people are unaware, but registries can also be used for other things aside from reunion. If a medical situation or diagnosis occurs within the birth family, they can register than info for the adoptee. They can include a contact preference as well. A birth family may want to relay pertinent info, but may not want to have any direct contact. Either way, if you are an adoptee it can be beneficial to you to be on the registries.